Motoyuki Hattori

SLC37A4 mediates glucose-6-phosphate transport for glucose homeostasis. Two recent studies in PLOS Biology report its structures and, together with other reports, illuminate the glucose-6-phosphate/phosphate exchange cycle and its inhibition mechanism.

Dimethylsulfoniopropionate (DMSP) is a ubiquitous marine organosulfur compound central to microbial stress responses, chemotaxis, and nutrient cycling. Its catabolism produces dimethylsulfide (DMS), a climate-active gas, and plays a key role in the global sulfur cycle. However, the molecular basis of DMSP import, underpinning its microbial metabolism, remains poorly understood. Here, we identify and characterize the BCCT-family transporter DddT from Psychrobacter sp. D2, a marine gamma-proteobacterium that utilizes DMSP as a carbon source. DddT is essential for DMSP uptake and functions as a Na ⁺ -coupled symporter driven by the transmembrane sodium gradient. Using cryo-electron microscopy, we determined DddT structures in multiple conformational states, revealing its Na ⁺ -dependent transport mechanism involving two sodium ions, one coordinated by a previously uncharacterized binding site. Sequence analysis shows that DddT-like proteins with conserved sodium-binding features are widespread in marine bacteria, suggesting this Na ⁺ -coupled transport mechanism represents a broadly conserved feature of the BCCT family. Our findings provide mechanistic insights into sodium-driven substrate uptake and marine sulfur cycling.

P2X receptors are ATP-gated cation channels, and the P2X3 subtype plays crucial roles in peripheral sensory neurons, including in chronic pain and chronic cough. Accordingly, P2X3 receptors have attracted substantial interest as a therapeutic target. Gefapixant, a negative allosteric modulator (NAM) of P2X3 receptors, has been approved in some countries for the treatment of chronic cough; however, its limited selectivity for P2X3 homomers over P2X2/P2X3 heteromers is associated with taste disturbance as a prominent adverse effect. These limitations have motivated the development of next-generation NAMs with improved subtype selectivity, but their subtype-specific allosteric inhibition mechanisms are unclear. Here, we report the cryo-EM structure of the human P2X3 receptor in complex with ATP and the P2X3-selective next-generation NAM sivopixant, an investigational drug. Sivopixant binds to an allosteric site at the portal of the central pocket in the extracellular domain, and structure-based mutational analysis by electrophysiology identifies key residues required for sivopixant-dependent inhibition of human P2X3 receptors. Structural comparisons across P2X subtypes, together with patch-clamp analyses of gain-of-function mutants that confer sensitivity to two investigational drugs, sivopixant and camlipixant, provided a broadly applicable structural framework for subtype selectivity. Furthermore, structural comparisons with apo and ATP-bound open states of P2X3 receptors, together with molecular dynamics simulations, revealed that sivopixant expands the upper-body domain to suppress the lower-body movements required for channel activation, thereby preventing channel opening even in the presence of ATP.

P2X receptors are ATP-gated cation channels, and the P2X3 subtype plays crucial roles in peripheral sensory neurons, including in chronic pain and chronic cough. Accordingly, P2X3 has attracted substantial interest as a therapeutic target. Gefapixant, a negative allosteric modulator (NAM) of P2X3, has been approved in some countries for the treatment of chronic cough; however, its limited selectivity for P2X3 homomers over P2X2/P2X3 heteromers is associated with taste disturbance as a prominent adverse effect. These limitations have motivated the development of next-generation NAMs with improved subtype selectivity, but their subtype-specific allosteric inhibition mechanisms are unclear. Here, we report the cryo-EM structure of the human P2X3 receptor in complex with ATP and the P2X3-selective next-generation NAM sivopixant, an investigational drug. Sivopixant binds to an allosteric site at the portal of the central pocket in the extracellular domain, and structure-based mutational analysis by electrophysiology identifies key residues required for sivopixant-dependent inhibition of human P2X3. Comparisons with P2X structures from other subtypes, together with gain-of-function mutants, define a structural basis for subtype-selective allosteric inhibition of the P2X3 receptor. Furthermore, structural comparisons with apo and ATP-bound open states of P2X3 receptors, together with molecular dynamics simulations, revealed that sivopixant expands the upper body domain to suppress the lower-body movements required for channel activation, thereby preventing channel opening even in the presence of ATP.

Despite intensive development, P2X7 modulators have struggled in translation due to human genetic variability and species-dependent drug responses. Here, we identify PSFL1191, a portal-of-central-pocket (PCP)-site inhibitor selective for human and panda P2X7, but inactive against rodents. Cryo-EM structures revealed two distinct PCP sub-pockets: PCP1, a rigid base pocket demanding precise steric complementarity with PSFL1191, and PCP2, a conserved middle cavity targeted by JNJ-54175446, a clinical candidate unaffected by species differences. Species selectivity maps to a deep PCP1 motif (V312-Y295-M105-F103-P96). In P2rx7 A312V/A312V mice, PSFL1191 markedly altered macrophagemediated bacterial clearance and wound healing while preserving basal physiology, effects absent in wild-type animals. Our findings establish the structural basis for interspecies pharmacological divergence in P2X7 modulation and highlight transgenic models as powerful tools for predicting therapeutic efficacy, thereby enabling more precise and efficient drug discovery.

Salicylic acid (SA) is a major defense phytohormone. In Arabidopsis thaliana , the isochorismate (IC) pathway is the primary route for pathogen-induced SA biosynthesis. First, the IC synthase (ICS) catalyzes the isomerization of chorismate to IC in chloroplasts. Second, the chloroplast-localized MATE transporter EDS5 appears to transport IC from chloroplasts to the cytosol. Cytosolic IC is then further converted to SA via the GH3 amino acid-conjugating enzyme PBS3. While this pathway is genetically well-characterized in A. thaliana , its evolutionary origin and conservation remain controversial. In this study, through comprehensive phylogenetic, structural, and functional analyses, we demonstrate that the IC pathway emerged within the Brassicales order in a time span between the divergence of Carica papaya and Capparis spinosa . The evolution of the IC pathway was driven by three key adaptations during the time span: 1) enhancement of ICS activity, 2) neofunctionalization of EDS5 after duplication of its ancestral gene, and 3) evolution of a PBS3 , whose activity is specialized for glutamate-conjugation to IC. Structural modeling and functional assays reveal that an enhanced salt bridge network in ICS enhanced its activity. One of the duplicated genes, EDS5, acquired key amino acid substitutions in the C-lobe, which contributed to the EDS5 neofunctionalization. In addition, the functional PBS3 clade, including A. thaliana PBS3 , is restricted to a Brassicales clade. Taken together, this study addresses the evolutionary trajectory of IC-based SA biosynthesis.

MgtE channels play crucial roles in Mg²⁺ homeostasis and are implicated in bacterial survival under antibiotic exposure. Previous structural and biophysical studies have predominantly focused on the Thermus thermophilus MgtE, leaving the structural and mechanistic diversity of MgtE family proteins largely unexplored. In this study, using a genome mining approach, we identified diverse MgtE homologs, including a novel subclass termed the “mini-N type,” which lacks the canonical cytoplasmic N and CBS domains but possesses a unique small N-like domain. Despite extensive expression screening, mini-N type homologs could not be stably purified. To address this issue, we designed a series of de novo proteins and determined their crystal structures. A selected de novo protein was fused to a mini-N type MgtE, enabling successful purification and preliminary cryo-EM imaging. Our findings demonstrate that de novo designed protein fusions can serve as powerful tools for stabilizing and purifying otherwise unstable membrane proteins, opening new avenues for the structural and functional studies of otherwise inaccessible membrane proteins.

Salicylic acid (SA) is a major defense phytohormone. In Arabidopsis thaliana , the isochorismate (IC) pathway is the primary route for pathogen-induced SA biosynthesis. First, the IC synthase (ICS) catalyzes the isomerization of chorismate to IC in chloroplasts. Second, the chloroplast-localized MATE transporter EDS5 appears to transport IC from chloroplasts to the cytosol. Cytosolic IC is then further converted to SA via the GH3 amino acid-conjugating enzyme PBS3. While this pathway is genetically well-characterized in A. thaliana , its evolutionary origin and conservation remain controversial. In this study, through comprehensive phylogenetic, structural, and functional analyses, we demonstrate that the IC pathway emerged within the Brassicales order in a time span between the divergence of Carica papaya and Capparis spinosa . The evolution of the IC pathway was driven by three key adaptations during the time span: (1) enhancement of ICS activity, (2) neofunctionalization of EDS5 after duplication of its ancestral gene, and (3) evolution of a PBS3 , whose activity is specialized for glutamate-conjugation to IC. Structural modeling and functional assays reveal that an enhanced salt bridge network in ICS enhanced its activity. One of the duplicated genes, EDS5, acquired key amino acid substitutions in the C-lobe, which likely contributed to the EDS5 neofunctionalization. In addition, the functional PBS3 clade, including A. thaliana PBS3 , is restricted to a Brassicales clade. Taken together, this study addresses the evolutionary trajectory of IC-based SA biosynthesis.

Machine learning (ML)–based design approaches have advanced the field of de novo protein design, with diffusion-based generative methods increasingly dominating protein design pipelines. Here, we report a “hallucination”-based protein design approach that functions in relaxed sequence space, enabling the efficient design of high-quality protein backbones over multiple scales and with broad scope of application without the need for any form of retraining. We experimentally produced and characterized more than 100 proteins. Three high-resolution crystal structures and two cryo–electron microscopy density maps of designed single-chain proteins comprising up to 1000 amino acids validate the accuracy of the method. Our pipeline can also be used to design synthetic protein-protein interactions, as validated experimentally by a set of protein heterodimers. Relaxed sequence optimization offers attractive performance with respect to designability, scope of applicability for different design problems, and scalability across protein sizes.